THE TRANSLOCATION OF PROTOPLASM 157 



enlarging vacuoles which soon fuse together and form one great 

 central vacuole bounded by a thin layer of hyaline protoplasm 

 pressed against the cell-wall. There can be but little doubt that 

 here, just as in Pyronema confluens and the Higher Fungi generally, 

 the evacuation of the labile protoplasm from the hyphae is accom- 

 plished by vacuolar pressure. 



In Rhizopus nigricans, terminal hyphae or systems of hyphae 

 which, after evacuating their contents, have been cut off by a sep- 

 tum usually live for some hours and, during this period, small 

 rounded highly refractive droplets looking like oil-drops can be seen 

 moving irregularly along the surface of the hyaline protoplasm 

 lining the cell-wall (Fig. 79, B, h). Finally, the hyphae die of 

 exhaustion. As they do so, they contract somewhat in diameter 

 and the movement of the droplets abruptly ceases (Fig. 79, F). 



In a mycelium of Rhizopus nigricans in which a rhythmic change 

 in direction of the streaming protoplasm was taking place about 

 every three or four minutes, it was observed : (1) that the vacuoles 

 in that part of the mycelium to which the protoplasm was flowing 

 were diminishing in size ; (2) that the vacuoles in that part of the 

 mycelium from which the protoplasm was flowing were increasing 

 in size ; and (3) that, when the current of protoplasm changed its 

 direction, the vacuoles which had decreased in size began to increase 



Fig. 79~cont. 



toward a developing sporangiophore and sporangium ; then, as shown at e, a 

 septum began to be formed as an annular ingrowth from the lateral wall ; at the 

 centre of the septum is a still large, but rapidly diminishing, aperture, through 

 which particles of protoplasm were seen to pass from the cell / to the cell g ; 

 h, small rounded highly refractive globules which move irregularly from place 

 to place along the surface of the layer of protoplasm lining the cell wall. 



C, 10 minutes after B : the septum, owing to annular ingrowth to the centre 

 of the hypha, has become complete, and now protoplasm can no longer pass 

 from/ to g ; the time taken from the beginning to the end of septum -formation 

 was about 20 minutes ; it will be seen that the septum has cut off a highly - 

 vacuolated part of the mycelium from a part which is filled with protoplasm. 



D, half an hour after C : the turgor pressure in the cell / has become greater 

 than that in the cell g, as is shown by the fact that the septum now bulges 

 convexly into g. E, half an hour after D : a large vacuole i has come into 

 existence in the cell g, and, presumably by its pressure, the protoplasm in g is 

 being evacuated. F, 24 hours after E : the cell / has died and collapsed, 

 its shrinkage is especially noticeable at j, its protoplasm has become dis- 

 organised, and its small rounded highly refractive granules have ceased to 

 move ; the cell g is still living, but the part in view, as a result of the growth 

 of the vacuole i, has evacuated all its massive protoplasm ; the living cell g, 

 by turgor pressure, has caused the septum to bulge convexly into the dead cell/. 

 Drawn by A. H. R. Buller and C. C. Neufeld. Magnification, 400 



